The present invention is drawn to methods and composition involving Clostridial neurotoxin derivatives having an enhanced ability to disrupt exocytosis of pain and/or inflammatory mediators from nociceptors or inducers of inflammation, thus preventing pain.
Botulinum neurotoxin (BoNT) serotypes A-G, produced by Clostridium botulinum, are the most potent poisons known due to specifically blocking the release of acetylcholine from peripheral nerves by proteolytically cleaving SNARE (“Soluble NSF Attachment Protein Receptors”) proteins, which mediate the fusion of the synaptic vesicle with the cell membrane, and are thus essential for Ca2+-stimulated exocytosis of neurotransmitters and pain peptides from the neuron.
The ability of Clostridial toxins such as, e.g., Botulinum neurotoxins (BoNTs) (including the BoNT serotypes BoNT/A, BoNT/B, BoNT/C1, BoNT/D, BoNT/E, BoNT/F and BoNT/G, as well as tetanus toxin TeTx) to inhibit neuronal transmission are being exploited in a wide variety of therapeutic and cosmetic applications, see e.g., Ward AB and Barnes MP, CLINICAL USERS OF BOTULINUM TOXINS (Cambridge University Press, Cambridge 2007). As an example, the BoNT/A-derived agent BOTOX® has been used in one or more countries for each the following indications: achalasia, adult spasticity, anal fissure, back pain, blepharospasm, bruxism, cervical dystonia, essential tremor, glabellar lines or hyperkinetic facial lines, headache, hemifacial spasm, hyperactivity of bladder, hyperhidrosis, juvenile cerebral palsy, multiple sclerosis, myoclonic disorders, nasal labial lines, spasmodic dysphonia, strabismus and VII nerve disorder.
There are Clostridial toxins other than the C. botulinum- and C. tetanus-derived toxins; these include, without limitation, the toxins of C. perfringins, C. septicum, C. difficile, C. spiroforme, C. butyricum and C. barati. However, it will be understood that in this specification a reference to “Clostridial toxins” or a similar reference, concerns the neurotoxins of C. botulinum subtypes and C. tetani subtypes, unless specifically or contextually indicated otherwise.
In addition, Clostridial toxin therapies are used or have been proposed for treating conditions including, without limitation,
a) neuromuscular disorders, see e.g., Kei Roger Aoki et al., Method for Treating Neuromuscular Disorders and Conditions with Botulinum Toxin Types A and B, U.S. Pat. No. 6,872,397 (Mar. 29, 2005); Rhett M. Schiffman, Methods for Treating Uterine Disorders, U.S. Patent Publication No. 2004/0175399 (Sep. 9, 2004); Richard L. Barron, Methods for Treating Ulcers and Gastroesophageal Reflux Disease, U.S. Patent Publication No. 2004/0086531 (May 7, 2004); and Kei Roger Aoki, et al., Method for Treating Dystonia with Botulinum Toxin C to G, U.S. Pat. No. 6,319,505 (Nov. 20, 2001);
b) eye disorders, see e.g., Eric R. First, Methods and Compositions for Treating Eye Disorders, U.S. Patent Publication No. 2004/0234532 (Nov. 25, 2004); Kei Roger Aoki et al., Botulinum Toxin Treatment for Blepharospasm, U.S. Patent Publication No. 2004/0151740 (Aug. 5, 2004); and Kei Roger Aoki et al., Botulinum Toxin Treatment for Strabismus, U.S. Patent Publication No. 2004/0126396 (Jul. 1, 2004);
c) pain, see e.g., Kei Roger Aoki et al., Pain Treatment by Peripheral Administration of a Neurotoxin, U.S. Pat. No. 6,869,610 (Mar. 22, 2005); Stephen Donovan, Clostridial Toxin Derivatives and Methods to Treat Pain, U.S. Pat. No. 6,641,820 (Nov. 4, 2003); Kei Roger Aoki, et al., Method for Treating Pain by Peripheral Administration of a Neurotoxin, U.S. Pat. No. 6,464,986 (Oct. 15, 2002); Kei Roger Aoki and Minglei Cui, Methods for Treating Pain, U.S. Pat. No. 6,113,915 (Sep. 5, 2000); Martin A. Voet, Methods for Treating Fibromyalgia, U.S. Pat. No. 6,623,742 (Sep. 23, 2003); Martin A. Voet, Botulinum Toxin Therapy for Fibromyalgia, U.S. Patent Publication No. 2004/0062776 (Apr. 1, 2004); and Kei Roger Aoki et al., Botulinum Toxin Therapy for Lower Back Pain, U.S. Patent Publication No. 2004/0037852 (Feb. 26, 2004);
d) muscle injuries, see e.g., Gregory F. Brooks, Methods for Treating Muscle Injuries, U.S. Pat. No. 6,423,319 (Jul. 23, 2002);
e) headache, see e.g., Martin Voet, Methods for Treating Sinus Headache, U.S. Pat. No. 6,838,434 (Jan. 4, 2005); Kei Roger Aoki et al., Methods for Treating Tension Headache, U.S. Pat. No. 6,776,992 (Aug. 17, 2004); and Kei Roger Aoki et al., Method for Treating Headache, U.S. Pat. No. 6,458,365 (Oct. 1, 2002); William J. Binder, Method for Reduction of Migraine Headache Pain, U.S. Pat. No. 5,714,469 (Feb. 3, 1998);
f) cardiovascular diseases, see e.g., Gregory F. Brooks and Stephen Donovan, Methods for Treating Cardiovascular Diseases with Botulinum Toxin, U.S. Pat. No. 6,767,544 (Jul. 27, 2004);
e) neurological disorders, see e.g., Stephen Donovan, Parkinson's Disease Treatment, U.S. Pat. No. 6,620,415 (Sep. 16, 2003); and Stephen Donovan, Method for Treating Parkinson's Disease with a Botulinum Toxin, U.S. Pat. No. 6,306,403 (Oct. 23, 2001);
g) neuropsychiatric disorders, see e.g., Stephen Donovan, Botulinum Toxin Therapy for Neuropsychiatric Disorders, U.S. Patent Publication No. 2004/0180061 (Sep. 16, 2004); and Steven Donovan, Therapeutic Treatments for Neuropsychiatric Disorders, U.S. Patent Publication No. 2003/0211121 (Nov. 13, 2003);
f) endocrine disorders, see e.g., Stephen Donovan, Method for Treating Endocrine Disorders, U.S. Pat. No. 6,827,931 (Dec. 7, 2004); Stephen Donovan, Method for Treating Thyroid Disorders with a Botulinum Toxin, U.S. Pat. No. 6,740,321 (May 25, 2004); Kei Roger Aoki et al., Method for Treating a Cholinergic Influenced Sweat Gland, U.S. Pat. No. 6,683,049 (Jan. 27, 2004); Stephen Donovan, Neurotoxin Therapy for Diabetes, U.S. Pat. No. 6,416,765 (Jul. 9, 2002); Stephen Donovan, Methods for Treating Diabetes, U.S. Pat. No. 6,337,075 (Jan. 8, 2002); Stephen Donovan, Method for Treating a Pancreatic Disorder with a Neurotoxin, U.S. Pat. No. 6,261,572 (Jul. 17, 2001); Stephen Donovan, Methods for Treating Pancreatic Disorders, U.S. Pat. No. 6,143,306 (Nov. 7, 2000);
g) cancers, see e.g., Stephen Donovan, Methods for Treating Bone Tumors, U.S. Pat. No. 6,565,870 (May 20, 2003); Stephen Donovan, Method for Treating Cancer with a Neurotoxin to Improve Patient Function, U.S. Pat. No. 6,368,605 (Apr. 9, 2002); Stephen Donovan, Method for Treating Cancer with a Neurotoxin, U.S. Pat. No. 6,139,845 (Oct. 31, 2000); and Mitchell F. Brin and Stephen Donovan, Methods for Treating Diverse Cancers, U.S. Patent Publication No. 2005/0031648 (Feb. 10, 2005);
h) otic disorders, see e.g., Stephen Donovan, Neurotoxin Therapy for Inner Ear Disorders, U.S. Pat. No. 6,358,926 (Mar. 19, 2002); and Stephen Donovan, Method for Treating Otic Disorders, U.S. Pat. No. 6,265,379 (Jul. 24, 2001);
i) autonomic disorders, see, e.g., Pankai J. Pasricha and Anthony N. Kalloo, Method for Treating Gastrointestinal Muscle Disorders and Other Smooth Muscle Dysfunction, U.S. Pat. No. 5,437,291 (Aug. 1, 1995);
j) as well as other disorders, see e.g., William J. Binder, Method for Treatment of Skin Lesions Associated with Cutaneous Cell-proliferative Disorders, U.S. Pat. No. 5,670,484 (Sep. 23, 1997); Eric R. First, Application of Botulinum Toxin to the Management of Neurogenic Inflammatory Disorders, U.S. Pat. No. 6,063,768 (May 16, 2000); Marvin Schwartz and Brian J. Freund, Method to Reduce Hair Loss and Stimulate Hair Growth, U.S. Pat. No. 6,299,893 (Oct. 9, 2001); Jean D. A. Carruthers and Alastair Carruthers, Cosmetic Use of Botulinum Toxin for Treatment of Downturned Mouth, U.S. Pat. No. 6,358,917 (Mar. 19, 2002); Stephen Donovan, Use of a Clostridial Toxin to Reduce Appetite, U.S. Patent Publication No. 2004/40253274 (Dec. 16, 2004); and Howard I. Katz and Andrew M. Blumenfeld, Botulinum Toxin Dental Therapies and Procedures, U.S. Patent Publication No. 2004/0115139 (Jun. 17, 2004); Kei Roger Aoki, et al., Treatment of Neuromuscular Disorders and Conditions with Different Botulinum, U.S. Patent Publication No. 2002/0010138 (Jan. 24, 2002); and Kei Roger Aoki, et al., Use of Botulinum Toxins for Treating Various Disorders and Conditions and Associated Pain, U.S. Patent Publication No. 2004/0013692 (Jan. 22, 2004).
Table 2, below, provides the amino acid sequences of isotypes of various currently known botulinum-related (BoNT and TeTX) Clostridial toxins. These toxins possess a minimum of approximately 35% amino acid identity with each other and share the same general functional domain organization and overall structural architecture. The naturally-occuring Clostridial toxins are each translated as a single chain polypeptide of approximately 150 kDa that is subsequently cleaved by proteolytic scission within a disulfide loop by a naturally-occurring protease, such as, e.g., an endogenous Clostridial toxin protease or a naturally-occurring protease produced in the environment. This post-translational processing yields a mature di-chain molecule comprising an approximately 50 kDa light chain (LC) and an approximately 100 kDa heavy chain (HC) held together by a single inter-chain disulfide bond and noncovalent interactions.
Each mature di-chain Clostridial toxin molecule comprises three functionally distinct domains: 1) an enzymatic domain located in the LC that includes a metalloprotease region containing a zinc-dependent endopeptidase activity which specifically targets one or more SNARE proteins that mediate the fusion of the synaptic vesicle with the cell membrane; 2) a translocation domain contained within the amino-terminal half of the H chain (termed “HN”) that facilitates release of at least the LC chain of the toxin from an endosome into the cytoplasm of the target cell; and 3) a binding domain found within the carboxyl-terminal half of the H chain (HC) that determines the binding activity and binding specificity of the toxin.
The HC comprises HCN and HCC sub-domains (the N- and C-terminal portions of HC, respectively). There is now substantial evidence that most or all BoNT/X toxins bind a target cell using a “dual receptor”, wherein the HC portion of the toxin comprising both HCN and HCC subdomains binds certain cell surface gangliosides and a protein receptor (perhaps glycosylated); binding of the protein receptor facilitates the internalization of the toxin within the cell. By “X” is meant any serotype of botulinum toxin. Although the term “BoNT/X” is generally used to indicate subtypes of botulinum toxin, the term may also include TeTX regions thereof. HCC binds the receptor complex located at the surface of the target cell.
It will be understood that there exist strains or subtypes of each serotype of these toxins; these may vary somewhat in their amino acid sequences, particularly (but not exclusively) in non-critical regions (so called “variable” regions) without a substantial change in the identity or activity characteristic of the indicated toxin or toxin domain.
In Table 1 below, the standard one-letter and three letter amino acid codes are provided:
TABLE 1Amino AcidThree letter codeOne letter codealanineAlaAarginineArgRasparagineAsnNaspartic acidAspDasparagine or aspartic acidAsxBcysteineCysCglutamic acidGluEglutamineGlnQglutamine or glutamic acidGlxZglycineGlyGhistidineHisHisoleucineIleIleucineLeuLlysineLysKmethionineMetMphenylalaninePheFprolineProPserineSerSthreonineThrTtryptophanTryWtyrosineTyrYvalineValV
TABLE 2Clostridial Toxin Reference Sequences and Regions(identified, from amino to carboxy direction;amino acid number to amino acid number)SEQ IDToxinNO:LCHNHCBoNT/A7M1-K448A449-K871N872-L1296BoNT/B8M1-K441A442-S858E859-E1291BoNT/C 19M1-K449T450-N866N867-E1291BoNT/D10M1-R445D446-N862S863-E1276BoNT/E11M1-R422K423-K845R846-K1252BoNT/F12M1-K439A440-K864K865-E1274BoNT/G13M1-K446S447-S863N864-E1297TeNT14M1-A457S458-V879I880-D1315
Those of ordinary skill in the art recognize that Clostridial subtype toxin variants may exist in nature, having variations in the amino acid sequences shown above (or in the nucleotide sequences encoding these amino acid sequences). As used herein, the term “naturally-occurring Clostridial domain variant” means any Clostridial domain (endopeptidase, translocation, and/or binding domains) produced by a naturally-occurring process, including, without limitation, Clostridial domain isoforms produced from alternatively-spliced transcripts, Clostridial domain isoforms produced by spontaneous mutations and Clostridial domain subtypes. As used herein, a naturally-occurring Clostridial domain variant functions in substantially the same manner as the reference Clostridial domain on which the naturally-occurring Clostridial domain variant is based, and can be substituted for the reference Clostridial domain in any aspect of the present invention.
A naturally-occurring Clostridial domain variant may substitute one or more amino acids, two or more amino acids, three or more amino acids, four or more amino acids, five or more amino acids, ten or more amino acids, 20 or more amino acids, 30 or more amino acids, 40 or more amino acids, 50 or more amino acids or 100 or more amino acids from the reference Clostridial domain on which the naturally-occurring Clostridial domain variant is based. A naturally-occurring Clostridial domain variant can also substitute at least 10 contiguous amino acids, at least 15 contiguous amino acids, at least 20 contiguous amino acids, or at least 25 contiguous amino acids from the reference Clostridial domain on which the naturally-occurring Clostridial domain variant is based, that possess at least 50% amino acid identity, 65% amino acid identity, 75% amino acid identity, 85% amino acid identity or 95% amino acid identity to the reference Clostridial domain on which the naturally-occurring Clostridial domain variant is based, so long as the biological or biochemical activity of the naturally-occurring Clostridial domain is substantially preserved. It will also be understood that conservative amino acid insertions and deletions can also be made so long as the characteristic function and identity of the domain is not substantially altered.
Due to the degeneracy of the genetic code, one of ordinary skill in the art will recognize that these amino acid sequences may be encoded by a finite set of different DNA molecules having different, but defined, nucleotide sequences. For example, degenerate nucleotide sequences encoding a given peptide or protein may have different codons adapted or selected to favor expression in a particular host cell. Using this information one can construct an expressible open nucleic acid reading frame for assembly of a nucleic acid molecule comprising any combination of these amino acid domain-encoding regions, either alone or with additional nucleic acid sequences, inserted into a suitable expression vector and subsequent expression within a chosen host cell. For example, International Patent Publication WO01/14570 discloses methods of making single-chain, cleavable recombinant modified or unmodified Clostridial neurotoxin derivatives and chimeric and hybrid forms thereof using such methods. Additional publications disclosing methods of making expressible recombinant neurotoxins and derivatives thereof include U.S. Pat. Nos. 5,989,545; 6,203,794; 6,395,513; U.S. Publication Numbers U.S. 2003/0166238; U.S. 2002/169942; U.S. 2004/176299; U.S. 2004/126397; U.S. 2005/035730; U.S. 2005/068494; U.S. 2006/011966; International Patent Applications WO95/32738; WO 99/55359; WO96/33273; WO98/07864; WO99/17806; WO98/07864; WO02/44199; WO02/40506, and U.S. patent application Ser. No. 13/644,386, filed Oct. 4, 2012. These and all other patents, patent publications, and non-patent publications cited in this patent application, whether or not specifically indicated as such, are hereby individually incorporated by reference as part of this specification.
The use of recombinant DNA techniques permits the construction of modified Clostridial neurotoxins having different or modified functional properties from the naturally-occurring toxin subtypes and strains thereof.
For example, altering the naturally-occurring amino acid sequence of the native neurotoxin light chain and/or adding a different therapeutic moiety permits the construction of transport proteins designed to carry a therapeutic agent within a neuron. See U.S. Pat. No. 6,203,794 (hereby incorporated by reference herein).
Altering the targeting (cell-binding) domain permits the toxin to be transported within pancreatic cells, such as acinar cells, thereby preventing secretion of activated digestive enzymes by such cells, See U.S. Pat. No. 6,843,998 (hereby incorporated by reference herein), or sensory afferent neurons, thereby preventing neurotransmitter, cytokine and pain peptide release and thus providing relief from pain; see U.S. Pat. No. 6,395,513 (hereby incorporated by reference herein.)
In addition, U.S. Pat. No. 7,422,877 (hereby incorporated by reference herein) discloses the creation of chimeric neurotoxin derivatives comprising, for example, the binding domain and the translocation domain (or modified versions thereof) of one neurotoxin subtype for example, BoNT/A, and the light chain region of another neurotoxin subtype, for example, BoNT/E. It will be seen that given the general structural homology between the neurotoxin subtypes, any combination of the three basic Clostridial neurotoxin domains, may be made in a single amino acid chain (or in cleaved di-chain molecules). Therefore, for example, a binding domain from any of neurotoxin subtypes A, B, C1, D, E, F, G, or TeTX may be independently combined with a translocation domain from neurotoxin subtypes A, B, C1, D, E, F, G, or TeTX, and further independently combined with a endopeptidase domain from any of neurotoxin subtypes A, B, C1, D, E, F, G or TeTX. This can be done, for example, by recombinant construction and expression of a single chimeric chain which is subsequently cleaved to yield the dichain toxin, or by separate expression of single H and L chains, which are then combined by, for example, creation of an interchain disulfide bond and subsequently purified. Furthermore, using such techniques, the activity of various domains may be altered (for example, mutations can be introduced in an LC domain to destroy the protease activity of the LC), or the naturally-occurring domains may be replaced with other moieties, as described elsewhere herein, where for example, the HC domain of BoNT/A (or a portion thereof) is mutated or deleted and a targeting ligand (TL) appended.
When discussing the three general neurotoxin domains of each Clostridial neurotoxin subtype (binding, translocation and endopeptidase), it will be understood that Clostridial neurotoxin research is a well-developed field, and the correlation of the amino acid sequences comprising each of these domains with their functions is well known. Reference to each of these terms (“translocation domain”, “binding domain”, and “protease”, “endopeptidase”, “LC” or “light chain” domain) shall be understood to include the corresponding domains contained in any of the amino acid sequences of Clostridial neurotoxin subtypes listed in SEQ ID NO: 7-14 as listed in Table 2, as well as conservatively modified and optimized variants of these sequences or domains within these sequences.
Additionally, the subdivision of these general domains into subdomains is also known. For example, the subdivision of binding domain HC into subdomains HCN (the amino-terminal portion of the domain, corresponding approximately to amino acids 871-1091 of BoNT/A) and HCC (the carboxy-terminal portion of the HC domain, corresponding approximately to amino acids 1092-1296 of BoNT/A) is also well known. See e.g., Lacy D B and Stevens R C, Sequence Homology and Structural Analysis of the Clostridial Neurotoxins, 1999, J. Mol. Biol. 291:1091-1104. Subdomain HCN is highly conserved among botulinum toxin subtypes, however, little is known about its function. The HCC subdomain is less conserved.
Additionally, the nucleotide and amino acid sequences of each of these domains and subdomains are known and have been disclosed in this specification, and therefore using this disclosure in combination with knowledge of the genetic code, nucleotide sequences encoding a protein to be expressed can be made. It would, of course, be a matter of routine for a person of ordinary skill in the art in view of this specification, to immediately envision other nucleotide sequences encoding the indicated polypeptides. Also, due to the redundancy of the genetic code, a finite number of nucleotide sequences are possible for each polypeptide. Further, it is clear that nucleic acids can be synthesized that comprise conservatively modified variants of these nucleotide sequences (or unique portions of them) in the region of homology containing no more than 10%, 8% or 5% base pair differences from a reference sequence.
Further, it will be understood that the amino acid sequences set forth in Table 2 and elsewhere in this specification or the associated sequence listing provide a full disclosure of any and all nucleotide sequences encoding these amino acid sequences and indicated regions thereof. A nucleotide sequence encoding an endopeptidase domain, translocation domain, or binding domain (including any subdomain) of a given neurotoxin subtype may respectively have 60% or greater, or 65% or greater, or 70% or greater, or 75% or greater, or 80% or greater, or 85% or greater, or 90% or greater, or 95% or greater, or 100% identity to any of such reference amino acid sequence regions listed in Table 2 or elsewhere.
Botulinum neurotoxins are expressed by Clostridial cells which also produce one or more non-toxin “neurotoxin associated proteins” or NAPs that non-covalently associate with the neurotoxin to form hemagglutinin complexes, also known as progenitor complexes. These NAPS help the neurotoxin resist protease degradation in the intestine when it is ingested in contaminated food.
The NAP proteins include three hemagglutinin (HA) proteins (HA1, HA2 and HA3), and a non-toxic, nonhemagglutinin protein (NTNH). BoNT types A2, E and F do not have the HA genes, and only produce a 12S (about 300 kDa) complex comprising BoNT and NTNH. “S” stands for Svedberg unit, a unit of centrifugal sedimentation rate. Types B, C and D produce 12S and 16S (about 500 kDa) complexes; the 16S complex includes BoNT, NTNH, HA1, HA2 and HA3. Type A1 has the 12S and 16S complexes plus a 19S complex of about 900 kDA, which may represent a dimer of 16S complexes.
Currently, BoNT/A1- and/B-hemagglutinin complexes have been approved for such clinical uses. The therapeutic benefits of BoNT/A1 complex are more persistent than that of BoNT/B due to its protease having a longer life-time in neurons.
As indicated above, BoNTs consist of a light chain-associated protease domain (LC) which is linked to a heavy chain (HC) through a single covalent disulphide bond and additional non-covalent bonds. A carboxy terminal (C-terminal) moiety of HC (HC) binds to its specific acceptors expressed on various nerve types, including motor, autonomic and sensory neurons. When bound to a target cell the BoNT molecule is transported into vesicles by endocytosis; the amino terminal (N-terminal) half of HC (HN) forms a channel that allows the LC to translocate from ‘endosomal-like’ membrane vesicles into the cytosol. Thereafter, the LC cleaves a specific SNARE protein substrate, thereby destroying the SNARE's ability to mediate vesicle-membrane fusion, and thus neurotransmitter, cytokine and pain peptide release from the cell.
The LCs of the various BoNT serotypes are similar, but not identical, and two different LCs may cleave different SNARE proteins, or cleave the same SNARE protein differently. For example, LC/A, LC/C, and LC/E cleave SNAP-25; LC/B, LC/D, LC/F, and LC/G cleave synaptobrevin-2 (VAMP-2); additionally, LC/C cleaves syntaxin, another SNARE protein which has been reported to be required for cell division. The LC of TeTx cleaves VAMP-2. The LCs of each serotype cleave their substrate at unique position in the molecule.
For example, the light chain of BoNT/A (LC/A) removes 9 amino acids from the C-terminus of SNAP-25, whereas the LC/E deletes a further 17 C-terminal residues and, thus, gives a more disruptive blockade of neuro-exocytosis by destabilising stable SNARE complexes (Meng et al., 2009; Wang et al., 2011). For example, the inhibition of neurotransmitter release by LC/A can usually be reversed by elevating Ca2+ influx, but not in the case of LC/E, presumably due to the greater destruction of the SNAP-25 substrate. However, despite the greater “robustness” of activity by LC/E, because LC/E induces only short transient neuromuscular paralysis, its clinical applications are limited.
It is highly desirable to create a therapeutic having new properties. For example, therapeutics in which two or more light chain endopeptidases derived from more than one serotype may combined in a BoNT or TeTx derivative in which each light chain is active and recognizes a different amino acid sequence in its substrate SNARE protein may be designed to target conditions like chronic pain, chronic inflammatory conditions (including arthritis), and/or conditions involving cytokine release.
In one example, a therapeutic is designed combining the powerful protease of LC/E combined with the long-lasting action of LC/A. This is particularly important for improving the efficacy of BoNT/A for treating chronic pain, including tension headaches/migraines, and chronic inflammatory diseases such as arthritis because BoNT/A complex on its own has been found to be effective in some, but not all, such patients. See e.g., Naumann M. et al. (2008) ASSESSMENT: BOTULINUM NEUROTOXIN IN THE TREATMENT OF AUTONOMIC DISORDERS AND PAIN (AN EVIDENCE-BASED REVIEW): REPORT OF THE THERAPEUTICS AND TECHNOLOGY ASSESSMENT SUBCOMMITTEE OF THE AMERICAN ACADEMY OF NEUROLOGY, Neurology 70:1707-1714 (hereby incorporated by reference herein). Blocking the exocytosis of pain-associated factors such as pain peptides and glutamate may prove useful in treating chronic pain, neuropathic pain and inflammatory conditions.
BoNT/A is unable to block the exocytotic release of pain-stimulating peptides [e.g. calcitonin gene-related peptide (CGRP) and substance P] from sensory neurons when elicited by activating TRPV1 (transient receptor potential vallinoid 1), a cation channel involved in the signalling of most forms of pain (Meng et al., 2007; Meng et al., 2009).
BoNT/E also fails to inhibit the capsasin-stimulated, TRPV1-mediated release of CGRP and substance P from sensory neurons, due to its cell surface acceptor (glycosylated synaptic vesicle protein 2A (SVP2A) and glycosylated SVP2B) being sparse or absent from the sensory neurons. However, a chimeric protein in which the HC (receptor-binding domain) of BoNT/E is replaced by its counterpart from BoNT/A is able to block the release of these pain-mediating peptides, indicating that the BoNT/A cell surface receptor facilitates the endocytosis and delivery of LC/E into nociceptive C-fibres.
Once inside the neuron, the LC/E protease, removes 26 SNAP-25 amino acid residues, thus preventing the formation of a stable SNARE complex required for neuro-exocytosis (Meng et al., 2009). Although LC/A also cleaves SNAP-25, it only cleaves 9 amino acid residues, and the blockage of exocytotic activity is less complete and stable.
In order to make it practical to clinically exploit such an advantageous feature of the LC/E protease, it is desirable to greatly extend its duration of action.